#include<stdio.h>
#include<math.h>

int main() {
	int a,b;
	scanf("%d %d",&a,&b);
	if(a>0)
		b = -b;
	else
		b = b*2;
	if(b%2 == -1 || b%2 == 1)
	{
		if(a*b>0)
			a = a;
		else
			a = -a;
	}
	if(b%2==0)
	{
		if(a*b>0)
			a = -a;
		else 
			a = a;
	}
	printf("%d",a-b);

	return 0;
}